Moisture indicating means and method



Jan. 1968 1.. w. HUBIN E AL 3,365,936

MOISTURE INDICATING MEANS AND METHOD Filed July 10, 1964 F ig.6.

Fig.7.

INVENTORS LORRIN W. HUBIN 8 TIMER EVERETT K MENTZER I /W F I g.8 reirATTORNE I United States Patent 3,365,936 MOISTURE INDICATING MEANSAND METHOD Lorrin W. Hubin, 1055 Waugh Drive, Hubbard, Ohio 44425, andEverett K. Mentzer, 1053 sequoya Drive, Youngstown, Ohio 44514 FiledJuly 10, 1964, Ser. No. 381,644 7 Claims. (Cl. 73-73) The presentinvention relates generally to sensing and indicating devices, and moreparticularly to a novel and improved means and method for sensing thepresence or absence of moisture in ceramic and the like structures.

Many applications exist wherein it becomes imperative to determine thequantity or absence of moisture in certain materials. Important amongthese applications is the determination or indication of the precisetime when certain materials have been completely dried in kilns, dryingovens, furnaces, or the like, in order to reduce the costs of the dryingprocess and to prevent damage to the materials being so processed.

A serious problem exists in the determination of moisture content inmaterials in high temperature environments, inasmuch as the sensingmeans thus employed is either rendered inaccurate by the ambienttemperature, or the sensing means conducts heat into the material toproduce localized drying effects and spurious indications of moisturecontent. Moreover, in certain forms of sensing means, the sensor itselfgenerates localized heating effects, which though small, becomesignificant when the sensing means is operated during relatively longperiods of certain drying cycles.

Accordingly, an object of the invention is the provision of a novel andefficient sensing means and method for indicating moisture content,which alleviate the aforementioned difficulties.

Another object is the provision of novel sensing means for indicatingmoisture content of a given material, which means is arranged so as tominimize the conduction of heat therethrough into the material from ahigh temperature environment.

A further object of the invention is the provision of a means and methodfor minimizing the local generation of heat through prolonged operationof certain forms of moisture sensing devices, as during dryingoperations.

Still another object of the invention is the provision of a moisturesensing device having means associated there with for indicating theexact moment when a material being dried becomes substantially oracceptably moisturefree.

An additional object of the invention is the provision of a novel andefficient circuit arrangement for operating the moisture sensing meansdisclosed herein and for providing visible indicia determinative ofmoisture content or lack thereof in a given material during its dryingcycle.

These and other objects of the invention are accomplished in accordancewith an illustrative embodiment of the invention, wherein a sensoryprobe for moisture indicating purposes is pressed into the materialbeing dried, if a soft porous structure, or is otherwise fitted into aclosely fitting recess therefor in the material. The probe includes apair of fiat metallic electrodes electrically separated but physicallyretained and preferably supported by a fiat insulative member insertedtherebetween. The electrodes are each provided with a uniqueconfiguration "ice which minimizes the transfer of heat *therealong whenthe probe and the material are placed in a high temperature environmentsuch as a drying furnace, or the like.

The sensory probe is arranged to operate under the effect ofelectrolytic action when moisture is present in the material, which ofcourse, requires the application of electric potential and the attendantgeneration of electrolytic currents when the material is notmoisture-free. In one embodiment of the invention, a circuit arrangementis associated with the sensory probe for pulsing the application ofpotential to the probe to avoid continuous generation of electrolyticcurrents and localized heating which would otherwise prematurely dry thematerial in the area of the probe. The flow of pulsed current throughthe probe can then be measured for a periodic indication of quantitativemoisture content until the material is completely dried. At such timethe end-point or termination of the drying cycle is indicated by thecircuit arrangement through the energization of suitable indicia, as:occasioned, in this example, by the absence of current flowing throughthe probe.

The foregoing and other objects, features and advantages of theinvention are elaborated upon during the forthcoming detaileddescription of the invention, when taken in conjunction with theaccompanying drawings wherein:

FIGURE 1 is a front elevational view, partly sectioned, of one form ofmoisture-sensing probe arranged in accordance with the invention;

FIG. 2 is a cross-sectional view of the probe of FIG. 1 taken alongreference line II-II thereof;

FIG. 3 is a cross-sectional view of the probe of FIG. 1 taken alongreference line III-III thereof;

FIG. 4 is a longitudinally sectioned view of the probe of FIG. 1 takenalong reference line IV-IV thereof;

FIGS. 5 and 6 are top and front elevational views respectively ofanother form of probe arranged in accordance with the invention;

FIG. 7 is an illustration of another embodiment of the sensing probe ofthe invention; and

FIG. 8 is a schematic circuit diagram of one form of supply andindication circuit arranged in accordance with the invention forsupplying a pulsed potential to a sensing device or other load device,for indicating moisture content quantitatively, and for providing anindication of moisture-freedom or zero current flow in the sensing orother load device.

Referring now with more specificity to FIGS. 1 to 4 of the drawings, theillustrative embodiment of the moisturesensing probe shown thereincomprises an electrically insulative holder 10, which is furtherarranged for supporting in spaced, insulated relation a pair of flatelectrodes 12 and 14. The holder 10, which can be fabricated from asuitable plastic or reinforced plastic material, is formed with acentral web portion 16 and thickened lateral edge portions 18. A pair ofopposed grooves 20 are provided respectively in the thickened portions18 adjacent each side of the web portion 15. Each pair of opposedgrooves is disposed and dimensioned to receive respectively the lateraledges of one of the electrodes 12 or 14 in sufficiently tight-fittingengagement to afford physical support therefor.

The probe thus formed is inserted into a moisture-retaining materialdenoted generally by the reference character 22. In an exemplaryapplication of the invention, the material 22 is a shaped mass ofdolomite, sawdust and a binder comprising sodium silicate. Such materialis used, for example, in the steel industry for covering crucibles toprevent too rapid cooling of the melt and to promote release of gasesfrom the melt. In this respect, it is essential that the porous dolomitestructure be absolutely dry to avoid deleterious interference with therelease of such gases and the possibility of explosion due to theformation of steam.

The dolomite or other moisture-bearing material can be dried in a kilnor drying oven or the like, and one or more of the probes of theinvention can be inserted into the moisture-bearing material while inthe kiln or oven to monitor the moisture content of the material duringthe desired drying cycle. In this manner, the precise residence time inthe kiln or oven can be determined so as to avoid over or under dryingof the material. When the moisture-bearing material is so placed, it isapparent that the metallic electrodes 12 and 14 of the probe willreadily conduct heat from the hot oven into that part of themoisture-bearing material immediately surrounding the probe and effectan accelerated drying condition, which will cause the probe to yield aspurious indication of dryness.

In order substantially to eliminate such spurious results and to renderthe probe useful in a high temperature environment, each of theelectrodes 12 or 14 is provided with a central necked-down or reducedportion 24, which reduces the flow of heat to the lower or activeelectrode portions 26 to a negligibly minimal amount. The electro-'lytic currents, then, are substantially limited to passage between thelower or active portions 26 of the electrodes 12 and 14, at least duringthe latter drydng stages in the kiln or oven.

The upper portions 28 of the electrodes 12 and 14 are of substantiallythe same shape as the lower, active portions 26 thereof to affordsymmetry to each electrode and permit insertion of either end first intothe moisturebearing material. Although the upper portions 28 can beeliminated, or replaced by upward extensions (not shown) of the reducedportions 24, provision of the similarly shaped upper portions 28 andlower active portions 26 is desirable to eliminate operator error inpositioning the probe in the material. After the probe is inserted intothe material to the desired depth, conductors 30 and 32 are afiixed tothe upper protruding ends (FIGS. 3 and 4) of the electrodes 12 and 14,respectively. The conductors can be connected to a suitable source ofpotential, or to the pulsed power supply circuit presently to bedescribed in connection with FIG. 8.

In FIGS. 5 and 6 an alternative form of moisture-sensing probe isillustrated. The latter probe is similar to that described above, exceptthat electrodes 12' and 14' are adhesively attached or otherwise securedto a fiat insulating support member 34. In this embodiment the lattermember is not formed with the grooved edge portions 18 of FIGS. 14.

In FIG. 7, an embodiment of the invention is shown which does notrequire a necked-down intermediate portion to prevent localized heatingat the test area. It again comprises an insulating board 35 havingelectrodes glued or otherwise secured to its opposite sides, only one ofsuch electrodes 37 being shown in FIG. 7. In this case, each electrodecomprises a thin foil of aluminum or other suitable metal having athickness on the order of about 0.002 inch. Aluminum foil, such as thatsold for household use in wrapping foods, will suifice. Preferably thebinder for holding the foil to the insulating board is sodium silicate.Alternatively, an aluminum-coated adhesive tape may be employed. Ineither case, the gage of the foil is such that it will not conductenough heat down into the body being dried to produce deleteriouseffects.

Referring now to FIG. 8 of the drawings, a pulsed supply circuit isshown and arranged in accordance with the invention for use with theaforesaid probe. The circuit includes a pair of supply busses 40 and 42connected to a source of potential via terminals 41 and 43. One of theconductors, conductor 40 for example, includes a seriesconnected,manually operated, on-oif switch 44. Con nected in series across thebusses 40 and 42 are a push button-type starting switch 46 and a startand run relay coil R1. When the start button 46 is released, the relaycoil R1 is locked in by a parallel path including its own contacts R11,a normally closed, pushbutton-type stop switch 48, and normally closedrelay contacts R4-1 (con trolled by relay coil R4 described below). Atthe same time, relay contacts R12 are closed by coil R1 to en ergizeboth the primary winding 50 of transformer and a relay coil R2, thefunction of which is described hereinafter. The energization of theprimary winding 50 can be indicated by a pilot lamp 54, if desired.

The secondary winding 56 of transformer 52 is connected to theelectrodes 12 and 14 of the probe described above through conductors 30and 32. As was explained, application of potential to the electrodes 12and 14 is pulsed to avoid the deleterious effects of localized drying,which would otherwise occur if the electrolytic currents through themoist material 22 were continuous.

The pulsed potential is effected by a suitably cammed timer switch 58having an appropriately shaped rise and dwell configuration (not shown)to conform to the aforementioned or other desired pulsation schedule.The timer switch 58, which is operated by timer motor 60, is connectedin series with pulsing relay coil R3 across the sup ply busses 40 and42. When energized by the timer switch 58, the relay coil R3 opens itsnormally closed contacts R3-1 which are connected in shorting relationacross the secondary winding 56. When so opened, the shorting eon= tactsR3-1 permit the secondary winding to deliver a pulse to the electrodes12 and 14. If desired, the flow of electrolytic current between theelectrodes 12 and 14 can be indicated by a sensitive ammeter 62, or thelike. The ameter 62 can be calibrated to indicate the moisture contentin suitable units.

As will be understood, it is desired to furnish visual indica, such asindicator lamp 64, which is energized only when the desired degree ofdrying is obtained. In this ex ample, the aforementioned supply circuitis further ar ranged to energize the indicator lamp 64 only when thematerial 22 is completely dry.

In'furtherance of this purpose, the indicator lamp 64 is connectedacross the supply busses 40 and 42 in series with relay contacts R4-2which are closed upon energization of indicator relay coil R4. The relaycoil R4 is of the slow dropout variety and is energized by timer switch58 upon closing of normally closed relay contacts R2-1 connected inseries with the relay coil R4. When there is moisture in the material22, however, the contacts R21 are held open by the aforementionedholding relay coil R2, which is energized with current flowing throughsecondary winding 56. Thus, relay coil R2 remains energized as long asmoisture remains in the material 22 and the resultant electrolyticcurrents impose a secondary load upon the primary winding 50 when theshorting relay contacts R3-1 are opened.

Energization of the indicator relay coil R4 also closes its contacts R43to lock in the relay coil R4. The contacts R43 are connected serially tothe stop button 48 in a parallel path relative to the timer switch 58and relay contacts R2-1. The thus energized relay coil R4 also opens itsnormally closed contacts R41 to deenergize the starting and runningrelay coil R1, which deenergizes the transformer 52. The indicator lamp64, then, remains on until the stop button 4-8 is actuated to deenergizethe indicator relay R4.

To recapitulate the operation of the invention, the electrodes 12 and 14are first inserted into the material to be dried and the start button 46depressed with the onofl? switch 44 closed. This action energizes relaycoil R1 which is held energized through its now-closed contacts R1-1 andthe contacts R4-1 of relay R4. Energization of relay coil R1 also closesits contacts R1-2, thereby energizing pilot lamp 54, the primary winding50 of transformer 52 and relay coil R2. Current now flows between theelectrodes 12 and 14, assuming that the material contains moisture. Atthe same time, the timer 60 periodically closes contacts 58, therebyperiodically energizing relay R3. When relay R3 is deenergized, contactsR3-1 are closed, thereby shorting the secondary winding 56 of thetransformer 52. However, when contacts R3-1 are open, current flowsbetween the electrodes 12 and 14, assuming that moisture is present inthe material.

When the material being dried is completely free of moisture, andassuming that relay contacts R3-1 are open, no current will flow betweenthe electrodes 12 and 14 and no current will flow in the secondarywinding 56 of transformer 52. Consequently, a back E.M.F. will bedeveloped in the primary winding 50 which will oppose the potentialbetween busses 40 and 42. As a result, the current through relay coil R2is reduced, causing it to drop out, thereby closing contacts R2-1. Whencontacts R2-1 close, the relay coil R4 becomes energized when contacts58 close, thereby opening contacts R41 and closing contacts R4-2 andR43. Opening of contacts R41 deenergizes relay coil R1, whereuponcontacts R1-2 open to deenergize the primary winding 50 and pilot lamp54. At the same time, closure of contacts R4-2 energizes indicator lamp64 to indicate that the material is dry; and contacts R4-3 hold relaycoil R4 energized until the stop pushbutton 48 is depressed. Whenpushbutton 48 is depressed, relay coil R4 become deenergized and thesystem is again ready for a moisture-sensing operation.

From the foregoing, it will be apparent that novel and efficient formsof a moisture-sensing probe and supply circuit therefor have beendisclosed herein. Inasmuch as the descriptive materials herein areexemplary and not limitative of the invention, it will be apparent thatnumerous modifications of the invention will occur to those skilled inthe art without departing from the spirit and scope of the invention.Moreover, it will be obvious that certain features of the invention canbe employed with out corresponding use of other features.

We claim as our invention:

1. A moisture-sensing probe for use in a high temperature environment,said probe comprising a pair of elongated generally planar electrodemembers, an elongated generally flat insulative member interposedbetween said electrode members, said insulative member having supportingmeans disposed along its lateral edges and supportingly engaging theadjacent lateral edges respectively of said electrode member, means ttorconnecting said members to a source of electric potential, said memberseach having a reduced portion between said connecting means and anactive portion of said electrode to minimize transfer of heat to saidactive portion.

2. A moisture-sensing probe for use in a high temperature environment,said probe comprising a pair of elongated generally flat electrodemembers, an elongated generally flat insulative member interposedbetween said electrode members and secured thereto, said electrodemembers each having an active electrode portion adjacent each endthereof and a reduced portion extending therebetween to minimizetransfer of heat between said active portions, and means coupled to anend of each of said electrode members for connecting said electrodemembers to a source of electric potential.

3. A moisture-sensing probe for use in a high temperature environment,said probe comprising a pair of elongated generally flat electrodemembers, an elongated generally flat insulative member interposedbetween said electrode members and supportingly secured thereto, saidelectrode members each having an active electrode portion adjacent eachend thereof and a reduced portion extending therebetween to minimizetransfer of heat between said active portions, the active electrodeportions of each electrode member being shaped and disposed on one abovethe other so that either end of the probe can be inserted, and meanscoupled to an end of each of said electrode members for connecting saidelectrode members to a source of electric potential.

4. A moisture-sensing probe for use in a high temperature environment,said probe comprising a pair of elongated generally planar electrodemembers, an elongated generally fiat insulative member interposedbetween said electrode members, said insulating member having thickenedlateral edge portions extending along its length, each of said thickenededge portions having a pair oi grooves disposed therein on oppositesides respectively of the flat surface of said insulative member forsupport;- ingly engaging the adjacent lateral edges respectively of saidelectrode members, means for connecting said members to a source ofelectric potential, said members each having a reduced portion betweensaid connecting means and an active portion of said electrode tominimize transfer of heat to said active portion.

5. A moisture-sensing probe for use in a high temperature environment,said probe comprising a pair of elongated generally planar electrodemembers, an elongated generally flat insulative member interposedbetween said electrode members, said insulative member having thickenedlateral edge portions extending along its length, each of said thickenededge portions having a pair of grooves disposed therein on oppositesides respectively of. the flat surface of said insulative member forsupportingly engaging the adjacent lateral edges respectively of saidelectrode members, said electrode members each having an activeelectrode portion adjacent each end thereof and a reduced portionextending therebetween tominimize transfer of heat between said activeportions, the active electrode portions of each electrode member beingshaped and disposed on one above the other so that either end of theprobe can be inserted, and means coupled to an end of each of saidelectrode members for connecting said electrode members to a source ofelectric potential.

6. The combination, with kiln means for drying to essentially completedryness a metallurgical hot top, of apparatus for determining when saidhot top is completely dry during drying of said hot top, comprising apair of electrodes adapted to be inserted Within said hot top when thehot top contains moisture, means for intermittently energizing saidelectrodes with an electrical potential at an energization repetitionrate which is independent of the amount of moisture in said hot top tominimize the drying effect of currents induced in the hot top betweensaid spaced electrodes, and means connected to said electrodes forindicating essentially complete dryness of said hot top when current nolonger flows through the hot top between said electrodes uponapplication of said electrical potential thereto.

7. The combination, with kiln means for drying to essentially completedryness a metallurgical hot top, of apparatus for determiningessentially complete dryness of said hot top during drying thereof,comprising a pair of electrodes adapted for insertion Within said hottop when the hot top contains moisture, means for intermittentlyenergizing said electrodes with an electrical potential at anessentially fixed energization repetition rate during dry of the hot topto minimize the drying eifect of currents induced in the hot top betweensaid spaced electrodes, and means connected to said electrodes forindicating essentially complete dryness of said hot top when current nolonger flows through the hot top between said electrodes uponapplication of said electrical potential thereto.

References Cited UNITED STATES PATENTS Ives 7373 Kott 7373 Dember73-3365 Higgins 324- 65 8 Bouyoucos 7373 Kaplan 32465 Peltola 73362Booth 73-17 RICHARD C. QUEISSER, Primary Examiner.

JAMES J. GILL, Examiner.

JAMES WILLIAMSON, Assistant Examiner.

6. THE COMBINATION, WITH KILN MEANS FOR DRYING TO ESSENTIALLY COMPLETEDRYNESS A METALLURGICAL HOT TOP, OF APPARATUS FOR DETERMINING WHEN SAIDHOT TOP IS COMPLETELY DRY DURING DRYING OF SAID HOT TOP, COMPRISING APAIR OF ELECTRODES ADAPTED TO BE INSERTED WITHIN SAID HOT TOP WHEN THEHOT TOP CONTAINS MOISTURE, MEANS FOR INTERMITTENTLY ENERGIZING SAIDELECTRODES WITH AN ELECTRICAL POTENTIAL AT AN ENERGIZATION REPETITIONRATE WHICH IS INDEPENDENT OF THE AMOUNT OF MOISTURE IN SAID HOT TOP TOMINIMIZE THE DRYING EFFECT OF CURRENTS INDUCED IN THE HOT TOP BETWEENSAID SPACED ELECTRODES, AND MEANS CONNECTED TO SAID ELECTRODES FORINDICATING ESSENTIALLY COMPLETE DRYNESS OF SAID HOT TOP WHEN CURRENT NOLONGER FLOWS THROUGH THE HOT TOP BETWEEN SAID ELECTRODES UPONAPPLICATION OF SAID ELECTRICAL POTENTIAL THERETO.